Mirabilite

Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the chemical formula Na₂SO₄·10H₂O. It is a vitreous, colorless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines. It is found around saline springs and along saline playa lakes. Associated minerals include gypsum, halite, thenardite, trona, glauberite, and epsomite.

Mirabilite
General
Category	Sulfate minerals
Formula (repeating unit)	Na2SO4·10H2O
Strunz classification	7.CD.10
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Identification
Formula mass	322.9 g/mol
Color	Colorless, white, yellowish-white, greenish-white
Crystal habit	Granular or well-formed coarse crystals
Twinning	Interpenetration twinning on {001}; also on {100}
Cleavage	{100} perfect, {001} poor, {010} poor
Fracture	Conchoidal
Mohs scale hardness	1.5–2
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent to opaque
Specific gravity	1.49
Optical properties	Biaxial (–), 2V=75.93°
Refractive index	nα = 1.396, nβ = 1.4103, nγ = 1.419
Birefringence	δ = 0.023
Pleochroism	none
Other characteristics	Not radioactive, non-fluorescent
References	[1][2][3]

Mirabilite is unstable and quickly dehydrates in dry air, the prismatic crystals turning into a white powder, thenardite (Na₂SO₄). In turn, thenardite can also absorb water and converts to mirabilite.

Mirabilite is used as a purgative in the Traditional Chinese medicine; in Mandarin, it is called máng xiāo. The name 'mirabilite' is based on the phrase "Sal mirabilis" (Latin for "wonderful salt") used by Johann Rudolph Glauber when he inadvertently synthesized mirabilite.[3][4]

Crystal structure of mirabilite